• Single-Family Lots: Homeowners on single-family lots can typically build one ADU and one JADU in addition to their primary residence. This offers significant potential for increasing housing on a single parcel.
• Multi-Family Lots: A major shift in 2025 comes with SB 1211, which now allows for up to eight detached ADUs on multi-family properties, provided they do not exceed the existing number of units within the main dwelling and meet setback and height requirements. This is a substantial increase from the previous limit of two detached ADUs and aims to unlock significant housing density in urban areas. Additionally, multiple ADUs can be created within the existing footprint of a multi-family dwelling.

• Standard ADU: Generally permitted up to 1,200 square feet. However, an attached ADU cannot exceed 50% of the primary dwelling's size or 1,200 square feet, whichever is smaller. Crucially, state law mandates that local agencies must permit an 800 sq ft ADU regardless of any more restrictive local size limits. Minimum sizes are also set: a one-bedroom ADU must be at least 850 sq ft, and a two-bedroom unit at least 1,000 sq ft.
• Junior ADU (JADU): Limited to a maximum of 500 square feet and must be contained entirely within an existing single-family residence.

State law generally limits side and rear setbacks for ADUs to a minimum of four feet. New provisions also make it easier to build an 800 sq ft ADU even if it doesn't meet front setback requirements, ensuring that lot size or existing conditions don't entirely preclude ADU development.

• Detached ADUs: Typically capped at 16 feet. However, this can extend to 18 feet if the property is within half a mile of public transit or on a lot with an existing or proposed multi-family dwelling. Some areas may permit up to 25 feet if the ADU is attached to the primary dwelling and adheres to the primary dwelling's zoning height limits.
• Attached ADUs: Generally follow the height restrictions of the primary residence but cannot exceed 25 feet.

One of the most significant relaxations in ADU regulations concerns parking. In many scenarios, no additional parking is required for ADUs, particularly if:

• The ADU is located within half a mile of public transit.
• The ADU is in a historically or architecturally significant area.
• A car-share vehicle is within one block.
• The ADU is built within an existing space (e.g., a garage or carport conversion).
• Parking replacement requirements are largely removed when existing parking is converted or demolished for an ADU.

A permanent and highly impactful change as of January 1, 2025, is the indefinite prohibition on local agencies imposing owner-occupancy requirements for ADUs. This means homeowners are no longer required to live in either the primary residence or the ADU to rent out the ADU, significantly increasing investment opportunities and housing availability. The only exception remains for properties with both an ADU and a JADU, where owner-occupancy of either the main residence or the JADU is still required by JADU law.

To ensure ADUs primarily serve as long-term housing solutions, California state law limits ADU rentals to a minimum of 30 consecutive days. Local governments may have additional regulations on short-term rentals beyond this state baseline.

Local agencies are mandated to approve or deny ADU permit applications within a brisk 60 days. If an application is denied, a comprehensive list of comments must be provided, allowing the applicant to address the issues. Crucially, if a city or county fails to meet this 60-day deadline, the permit is automatically deemed approved. ADU applications must also be approved ministerially, without the need for discretionary review or public hearings, provided they meet state and local standards.

Fire sprinklers are generally not required for the primary dwelling when constructing an ADU, unless the primary residence already has a sprinkler system installed. However, newly constructed ADUs may still be subject to fire protection standards related to water supply and fire department access.

A groundbreaking change allowing homeowners to potentially sell their ADUs separately from the main residence, treating them like condominiums. Assembly Bill 1033 (AB 1033), effective January 1, 2024, enables cities and counties to adopt ordinances permitting this. While a significant step towards increasing affordable homeownership options, its implementation depends on local government adoption, meaning it's not universally available across all jurisdictions yet.

For the thousands of existing, unpermitted ADUs across California, Assembly Bill 2533 (AB 2533), effective January 1, 2025, provides a clearer pathway to legalization. This legislation makes it easier for homeowners to bring non-compliant units up to code if they were built before January 1, 2020. Local building departments are required to approve legalization if the unit meets health and safety standards, without imposing excessive fees or penalties.

To further simplify and expedite the ADU development process, Assembly Bill 1332 (AB 1332) requires all California cities and counties to establish a program for pre-approved ADU plans by January 1, 2025. These plans, already vetted for compliance, aim to reduce design costs and streamline permitting for homeowners choosing from these standardized options.